Placoderms are a class of armored prehistoric fishes which lived first appeared in the Silurian (443.8-419.2 million years ago). Their head and thorax are covered by articulated armored plates and the rest of the body is scaled or naked, depending on the species. Placoderms were among the first jawed fish; their jaws likely evolved from the first of their gill arches.

It is unknown exactly how they managed to survive for so long.

PSEUDOTETRAPODS- Non-tetrapod vertebrates which evolved the ability to crawl on land separately from the ancestors of true tetropods

ARTHRODIRA
Arthrodira ("jointed neck") were the most diverse and numerically successful of the placoderm orders, occupying roles from giant apex predators to detritus-nibbling bottom dwellers. They had a movable joint between armor surrounding the head and body. As the lower jaw moved down the head shield moved, allowing for a larger opening. All arthrodires, save for Compagopiscis, lacked teeth, and used instead the sharpened edges of a bony plate, termed a "tooth plate," as a biting surface (Compagopiscis had true teeth in addition to tooth plates). The eye sockets are protected by a bony ring, a feature shared by birds and some ichthyosaurs. Early arthrodires, such as the genus Arctolepis, were well-armored fishes with flattened bodies. The largest member of this group, Dunkleosteus, was a true "superpredator" of the latest Devonian period, reaching 3 to as much as 9 meters in length. In contrast, the long-nosed Rolfosteus measured just 15 cm. Arthrodires are live-birthing fish.

False Lobe-Fin

Native to Tapiri's rivers, the False Lobe-fin will eat nearly anything, and their fleshy fins allow them to crawl up on land briefly to nab unsuspecting animals on the shore.

A-Mi-Kuk

Native to the coast of North Griffonia, these amphibious Pseudotetrapods eat whatever comes to the waters edge along with fish and aquatic animals. They are able to leave the water only breifly, and must return to the water as soon as they can or they dry out and die.

Rockcruncher

Native to Jurassica, the Rockcruncher is slower than other marine predators in its habitat, but has the most powerful bite of all of them, able to crunch stones, as its name implies.

Ziphius

A massive creature native to the Grey Ocean, the Ziphius tends to focus on slow-moving prey or carcasses, which can lead it to attack boats

Helmet Fish

Native to Concordia's coasts, the Helmet fish is a small but fierce predator.

Boilfish

A native of the simmering sea, the Boilfish is able to withstand high temperatures, and can actually spit out scalding water at aerial prey

Panzerfish

A slow-moving native of Stirrope's coastal waters.

Skullfish

A native of the Great Pelagic Ocean, this is a predatory fish that mainly focuses on small prey

Hydermis

A fast-moving shark analogue native to the Emerald Sea

Warrior Fish

Small predators native to Neighpon, these colorful fish are highly territorial, and are often captured for the (illegal) sport of "fish fighting"

Abyssal Shearjaw

A large marine predator which mainly eats giant squid, though it has been known to compete with the Abyssal Megalodon

Guerillafish

An ancient Lemurian bioweapon, the Guerillafish is a formidable guard beast with its sheer bulk, heavily armored cranium and massive, plate-like teeth, capable of neatly snipping prey into pieces. When all else fails, the beast unleashes a chilling sonic howl capable of rupturing internal organs at close range. These fish enjoy having to crack open armored meals such as whelks or coconuts, often resting on a heap of discarded shells and crunching them apart as a territorial display.

False Lusca

Found frequenting the same areas as the Lusca, this fish differs in habit from its shark neighbor by simply being an ambush predator, snapping up any prey which wanders withing range of its glowing lure.

Muskfish

A native of Tapiri's rivers, the muskfish is named after its strong smell, which it uses for communication in the murky waters where it lives. It's barbels are extremely sensitive to touch and are the fishes main way of finding food. The two larger ones on the sides of it's head are also covered in chemoreceptors, and can "taste" the waters around them.

Pseudophyseter

A deep-diving giant native to the Grey Ocean, the Psuedophyseter is a peaceful giant, though it can be vicious when hunting its preferred prey- Squids and other Placoderms.

Beetlefish

Native to the Emerald Sea and the Great Coastal Expanse, this fish is a semi-amphibious predator, pushing itself up on its pectoral appendages into a rearing posture to lunge at prey or snap defensively at predators.

ANTIARCHI
Antiarchi ("opposite anus") were the second most successful order of placoderms known, after the Arthrodira. The order's name was coined after incorrectly identifying the first fossils as being those of an armored tunicate, mistakenly thought the eye-hole was the mouth, and the opening for the anal siphon was on the other side of the body, as opposed to having both oral and anal siphons together at one end. The front portions of their bodies were heavily armored, to the point of literally resembling a box with eyes, with the sometimes scaled, sometimes naked rear portions often becoming sinuous, particularly with later forms. The pair of pectoral fins were modified into a pair of caliper-like, or arthropod-like limbs. In primitive forms, such as Yunnanolepis, the limbs were thick and short, while in advanced forms, such as Bothriolepis, the limbs were long and had elbow-like joints.

Turtlefish

This native of the Emerald Sea is a peaceful fish, both eating jellyfish in the open water and grazing the seabed for hard-shelled mollusks.

Pincermouth

a terrestrial pseudotetrapod, this native of the Everfree Forest is unusual not for its land-dwelling habits (as several other placoderms have evolved similarly), but because, like the Lucknoun of the Unnamed Southern Continent and the Greyface Owl of southern Equus, these fish appear to be on the road to true sapience.

Buglizard

An amphibious herbivore native to Lemuria

Arrowshield

A predator native to Lemuria, the "armor" covering this pseudotetrapod's cephalothorax is actually very thin, more like ossified scales than the heavy shell of its ancestors. It gives it rigidity and makes it more aerodynamic, like an arrowhead. Also the color markings differentiate between individuals of the same group, and the fin-like structure on its back is used for display during mating season. Males like this one are more colorful than females.

Placoptero

Native to Tapiri, this fish's shield has extended into a stiff, tail-like structure, while its tail and two of its fins have adapted into grasping legs

Lemurian Airstriker

Shown here preying on several Fishdeer (herbivores derived from a group of fish known as acanthodians), the Lemurian Airstriker is an aerial predator.

Mantissnake

Predators native to the Emerald Sea, these placoderms’ hard-shelled pectoral fins are adapted for catching and gripping prey. They are mostly ambush-hunters but some pelagic species actively pursue their prey with the aid of their strong, unarmored tails. The other species mostly use their tails to dig burrows into soft sediment or to hold on to vegetation while waiting for prey to get close enough to strike

Snakebeak

A slow-moving predator native to waters around Hosstralia.